Final answer:
Walter Garstang's hypothesis of vertebrate evolution could be described as punctuated equilibrium, which suggests that species remain constant for long periods of time and that change, when it occurs, is rapid.
Step-by-step explanation:
The hypothesis of Walter Garstang's vertebrate evolution could be described as punctuated equilibrium. This model suggests that species remain constant for long periods of time and that change, when it occurs, is rapid. The fossil record supports this model, showing long periods of stasis followed by bursts of rapid change. While intermediary forms do exist, the scarcity of them in the fossil record has led to the conclusion that punctuated equilibrium is the dominant theory.